1. Field of the Invention
The present invention relates to an endoscope system and endoscope external control device and, in particular, to an endoscope system and endoscope external control device for serial transmission of an imaging data from a solid-state imaging element mounted at the tip of an insertion part of an endoscope to a processor device.
2. Description of the Related Art
An endoscope system is generally configured to include an endoscope having an insertion part to be inserted inside a body cavity and a hand-held operating part to be held by an operator for performing various operations and a processor device (an external control device) to be connected via a universal cable extending from the endoscope. An imaging device is mounted at the tip of the insertion part of the endoscope, and an observed image captured by the imaging device is transmitted as an imaging signal to the processor device through the insertion part and the hand-held operating part of the endoscope and a signal line passing through the inside the universal cable, and is then subjected to various image processes in the processing device and is displayed on a monitor.
Japanese Patent Application Laid-Open Nos. 2002-065601 and 2009-201540 suggest that serial transmission is used as a method of transmitting an imaging signal from the imaging device of the endoscope to the processor device. According to these gazettes, compared with the case in which an imaging signal is transmitted as an analog signal, the transmission is less prone to be influenced by noise and transmission characteristics can be improved. Also, compared with the case in which an imaging signal is transmitted as a parallel signal, the number of signal lines can be reduced (that is, the diameter of the insertion part of the endoscope can be reduced), and the transmission speed can be increased (that is, the image quality of the shot image can be increased).
Also, Japanese Patent Application Laid-Open No. 2009-201540 suggests that since the transmission distance from the imaging device of the endoscope to the processor device is long in the above-described endoscope system, if a clock signal in synchronization with the imaging signal is also transmitted from the solid-state imaging element to the processor device together with the imaging signal with application of high-speed serial transmission technology, a timing skew occurs due to a difference in parasitic capacitance and wiring resistance associated with various signal lines for each of the imaging signal and the clock signal, thereby making transmission of the imaging signal unstable and resulting in an occurrence of an erroneous data detection in the processor device to disadvantageously degrade image quality. Furthermore, Japanese Patent Application Laid-Open No. 2009-201540 suggests that the imaging signal is converted to a serial signal in the imaging device by encoding by an 8B10B encoder, embedding a clock signal in the imaging signal so that a period in a Low or High state is three clocks or less, and extracting the clock signal from the imaging signal by a clock data recovery circuit (a CDR circuit) in the processor device, thereby solving the problem of a timing skew and achieving high-speed, stabilized serial transmission of the imaging signal.